The Association of Chief Police Officers has defended the use of tasers after
it emerged officers used a 50,000-volt device to shoot a 12-year-old girl.

The girl was armed with two knives and behaving aggressively towards officers when the device was fired to "prevent serious harm to both her, the public and the officers" in July 2011, Merseyside police said.

Deputy Chief Constable Simon Chesterman, The Association of Chief Police Officer's (ACPO's) lead for armed policing, admitted the use of Tasers on children "sounds awful" but stressed the weapons remain the "quickest, easiest and least injurious" measure to stop people posing a threat to the public.

However, addressing concerns that the weapons were being fired at young people, Mr Chesterman warned against using Tasers as an "easy option" to tackle people threatening to harm themselves.

"I'm not saying Tasers are risk free ... but the risk from the electricity is very low," he said.

"If there was a mission creep, where officers used it as the easy option to deal with something, that would cause me concern. It's not a compliance tool."

He added: "When you hear a 12-year-old being Tasered, it sounds awful. It doesn't mean it wasn't lawful, but it does sound bad.

"From what I've read about that particular case, the individual was intent on self-harming. It may well be that Taser saved her life."

Speaking at a briefing at ACPO's headquarters in central London, Mr Chesterman said he had some concerns about the use of "drive-stunning", where the Taser is held directly against a person's body.

When used in this mode, the weapon causes increased pain rather than "neuromuscular incapacitation" by disrupting the voluntary control of muscles.

Combustion had also occurred in "very rare cases" when Tasers were fired and officers are warned of the increased risk associated with using CS spray, Mr Chesterman added.

An forthcoming report by the Independent Police Complaints Commission (IPCC) is expected to address concerns about Tasers being used on people with mental health issues and those threatening self harm.

Many forces across England and Wales are expected to reveal a "significant increase" in their use of the weapons since 2009 when Home Office figures are published at the end of the month.

They are equipped with the X26 Taser which has a peak voltage of 50,000 volts when discharged but drops to 1,200 volts while travelling around the body at a current of 0.0021 amps.

About 8,000 additional Tasers were introduced to police forces between 2009 and 2010, ACPO said.

Nearly 13,800 officers across 43 forces in England and Wales are trained to use the weapons – about 10% of the total force.

The Police Federation has called for every front line police officer to be equipped with the guns.

But ACPO has said the number of trained officers is currently "about right", with plans to increase numbers in forces covering more remote, rural areas.

The Home Office is now considering whether forces should use the X26P Taser or the X2 version, which has a two-shot cartridge and a system to record the exact level of electricity used.